Six hundred U.S. troops are headed for Poland and the three Baltic countries for live-ammunition infantry exercises with armed forces from the four former Soviet-bloc nations.

Adm. John Kirby, the Pentagon press secretary, said Tuesday that the dispatch of troops from U.S. bases in Italy and Germany for military maneuvers near Russia’s western border is in response to its aggression in Ukraine.

“If there’s a message to Moscow, it is the exact same message (as delivered before), that we take our obligations very, very seriously on the continent of Europe,” Kirby told reporters at the Pentagon.

The American troops will be in Poland, Latvia, Estonia and Lithuania by Monday and that more American forces could be sent to other NATO nations in the future, Kirby said.

“These exercises were conceived and added to the (regular) exercise regime as a result of what’s going on in Ukraine,” Kirby said.

He said the first 600 troops, which will be drawn from the 173rd Infantry Brigade Combat Team (Airborne) headquartered in Italy, will conduct month-long exercises with about 150 airborne soldiers assigned to each of the four countries. That first group will be replaced in a month by a similar-sized contingent divided among the four nations, with subsequent rotations planned each month for the rest of the year.

“What we’re after here is a persistent presence _ a persistent rotational presence in these exercises,” Kirby said.

Russian troops began seizing control of Crimea, a peninsula in southeastern Ukraine with a Russian naval port, early last month. Russia claimed to have annexed Crimea, which has a majority ethnic-Russian population, as a result of a March 16 referendum in the region. The United States, along with many other governments and the United Nations, has not recognized the results of the referendum.

The United States last month stepped up its participation in NATO air patrols over the Baltics and in NATO training of Polish military pilots. But Kirby said the new troop movements are U.S.-bilateral exercises beyond the auspices of the transatlantic military alliance.

Meanwhile, Vice President Joe Biden on Tuesday met with Ukrainian Prime Minister Arseniy Yatsenyuk and Ukrainian legislators during a visit to the former Soviet republic.

“The road ahead is difficult,” Biden said at a news conference with Yatsenyuk in the Ukrainian capital of Kiev. “But you will not walk this road alone. We will walk it with you.”

Biden called on Russia to pull back thousands of troops massed on the Ukrainian border and to “stop supporting men in masks in unmarked uniforms” who have seized buildings in eastern Ukraine.

“No nation has the right to simply grab land from another nation,” he said. “No nation has that right. And we will never recognize Russia’s illegal occupation of Crimea, and neither will the world.”

The White House on Tuesday announced $8 million in non-lethal assistance to Ukrainian armed forces and border guards, plus $50 million for voter education and election oversight programs, governance advisers and energy security experts.

Ukraine is not a NATO member. Poland joined the military alliance in March 1999, more than seven years after the demise of the Soviet Union. Estonia, Latvia and Lithuania became members in March 2004.

Responding to reporters’ questions, Kirby denied that the absence of other NATO members in the infantry exercises reflects a reluctance among some European governments to escalate tensions with Russia over Ukraine.

“It’s not at all designed to indicate unwillingness by any other NATO partners,” Kirby said.

But with NATO having ruled out military intervention in Ukraine, Kirby said the series of U.S.-bilateral exercises was not merely symbolic.

“Any time you put troops on the ground and doing exercises _ in this case, for a month at a time _ it’s more than symbology,” he said. “The kind of work that we’re going to be doing is real infantry training. And that’s not insignificant.”

Asked whether Pentagon leaders believe that Russia represents a real threat to the Baltic nations or to Poland, Kirby, referring to Russian President Vladimir Putin, responded: “As for Russia and their intentions, I think you need to ask President Putin what his intentions are. What I’ll tell you is that nothing we’ve seen out of Moscow, nothing we’ve seen out of Russia or their armed forces, is de-escalating the tension, is making things any more stable in Ukraine or on the continent of Europe.”

Kirby said the Pentagon informed NATO of its plans for the infantry exercises but did not seek approval from the Western alliance. The Pentagon did not notify Russian military officials about the exercises, Kirby said.

NATO leaders in Brussels last week said the alliance will send more ships, planes and troops to the three Baltic countries and to Poland.

NATO, however, rejected Poland’s request to establish new permanent bases in the eastern European country.